9.1.3 Setting guidelines M13355-3 v8All the frequency and voltage magnitude conditions in the system where SAPTUF (81)performs its functions should be considered. The same also applies to the associatedequipment, its frequency and time characteristic.There are two specific application areas for SAPTUF (81):1. to protect equipment against damage due to low frequency, such as generators,transformers, and motors. Overexcitation is also related to low frequency2. to protect a power system, or a part of a power system, against breakdown, byshedding load, in generation deficit situations.The under frequency pickup value is set in Hz. All voltage magnitude related settingsare made as a percentage of a global base voltage parameter. The UBase value shouldbe set as a primary phase-to-phase value.Some applications and related setting guidelines for the frequency level are givenbelow:Equipment protection, such as for motors and generatorsThe setting has to be well below the lowest occurring "normal" frequency and wellabove the lowest acceptable frequency for the equipment.Power system protection, by load sheddingThe setting has to be below the lowest occurring "normal" frequency and well abovethe lowest acceptable frequency for power stations, or sensitive loads. The settinglevel, the number of levels and the distance between two levels (in time and/or infrequency) depends very much on the characteristics of the power system underconsideration. The size of the "largest loss of production" compared to "the size of thepower system" is a critical parameter. In large systems, the load shedding can be set ata fairly high frequency level, and the time delay is normally not critical. In smallersystems the frequency pickup level has to be set at a lower value, and the time delaymust be rather short.The voltage related time delay is used for load shedding. The settings of SAPTUF (81)could be the same all over the power system. The load shedding is then performedfirstly in areas with low voltage magnitude, which normally are the most problematicareas, where the load shedding also is most efficient.9.2 Overfrequency protection SAPTOF (81) IP15747-1 v3Section 9 1MRK 505 370-UUS AFrequency protection262 Busbar protection REB670 2.2 ANSIApplication manual
